An internal combustion engine of the stated type is used as a motor vehicle drive unit. Within the context of the present disclosure, the expression “internal combustion engine” encompasses diesel engines as well as Otto-cycle engines and hybrid internal combustion engines, e.g., internal combustion engines that are operated using a hybrid combustion process. Hybrid engines may also use hybrid drives which comprise an electric machine in addition to the IC engine which may be connected in terms of drive to the internal combustion engine, receiving power from the internal combustion engine or which, as a switchable auxiliary drive, additionally outputs power.
In the development of internal combustion engines, it is desirable to minimize fuel consumption. Furthermore, a reduction of the pollutant emissions is sought in order to comply with future limit values for pollutant emissions. Thus, internal combustion engines are therefore ever more commonly being equipped with a supercharging arrangement, where supercharging is primarily a method for increasing power. Charge air for the combustion process in the engine is compressed, resulting in a supply of a greater mass of charge air to each cylinder per working cycle. In this way, the fuel mass and therefore the mean pressure may be increased.
Supercharging may increase the power of an internal combustion engine while maintaining an unchanged swept volume, or reduce the swept volume while maintaining the same power. Supercharging leads to an increase in volumetric power output and a more expedient power-to-weight ratio. If the swept volume is reduced, given the same vehicle boundary conditions, the load collective may be shifted toward higher loads, at which the specific fuel consumption is lower. Supercharging of an internal combustion engine consequently assists in minimizing fuel consumption, improving the efficiency of the internal combustion engine.
For supercharging, use is often made of an exhaust-gas turbocharger, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust-gas flow is fed to the turbine and expands in the turbine with a release of energy, as a result of which the shaft is set in rotation. The energy released by the exhaust-gas flow to the turbine and ultimately to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor conveys and compresses the charge air fed to it, as a result of which supercharging of the cylinders is obtained. A charge-air cooler (CAC) may be arranged in the intake system downstream of the compressor, that cools the compressed charge air before it enters the cylinders. The CAC lowers the temperature and thereby increases the density of the charge air, so that the cooling effect of the CAC improves charging of the cylinders, by allowing a greater air mass to be delivered. Compression by cooling takes place.
However, the cooling of the combustion air may give rise to problems. During the course of the cooling, liquids previously contained in the combustion air still in gaseous form, in particular water, may condense out if the dew point temperature of a component of the gaseous air flow is undershot or the air is saturated. If the precipitated condensate is not continuously discharged, and supplied to the cylinders, in extremely small quantities, for example owing to the kinetics of the air flow or by means of a suitable arrangement or configuration of the charge-air cooler used, condensate may collect in the charge-air cooler and/or in the intake system downstream of the charge-air cooler. The condensate may be abruptly introduced into the intake system from the CAC in an unpredictable manner and in relatively large quantities, for example in the presence of lateral acceleration as a result of cornering, or when traveling on a gradient or over a bump. The latter is also referred to as water hammer, which may lead not only to a severe disruption in the operation of the internal combustion engine but also lead to degradation of components downstream of the CAC.
The issue described above may be further intensified if the combustion air contains recirculated exhaust gas. By increasing the recirculated exhaust-gas (EGR) flow rate, fractions of the individual exhaust-gas components in the combustion air, and in particular of water contained in the exhaust gas, may increase. In the prior art, therefore, the EGR flow rate is in some cases limited in order to reduce the amount of condensed water or to prevent condensation.
The formation of condensate may be promoted by a high humidity of the ambient air and low ambient temperatures, where, in the presence of low ambient temperatures, in particular temperatures below the freezing point, ice may form, e.g., condensed water freezes in the intake system. If ice particles or ice deposits form in the CAC, the flow resistance of the cooler in the intake system increases, and pressure loss across the cooler increases, reducing the efficiency of the supercharged internal combustion engine.
Various attempts to address the formation of ice within the CAC include methods to increase the temperature of the CAC. On example approach is shown by Wolf in DE Patent Application 10,2008028,194. Therein, a pressure difference across a charge-air cooler is determined to infer the icing state of the charge-air cooler. If icing of the charge-air cooler is identified, the ice situated in the charge-air cooler may be melted by increasing the charge-air temperature at the cooler inlet, and thus the pressure loss across the cooler may be reduced. The inlet temperature of the air may be increased by various methods, for example, by increasing the pressure of the inflowing air and/or reducing the cooling power of the cooler.
Another example approach to address icing of the CAC is shown by in U.S. Pat. No. 9,109,505. Therein, an engine system including a turbocharger compressor with a compressor bypass may couple an outlet of a CAC downstream of the compressor to the compressor inlet. A compressor recirculation valve (CRV) is disposed in the compressor bypass, controlling gas flow through the bypass. During conditions leading to ice formation in the CAC, the CRV is opened in conjunction with closing an exhaust turbine wastegate. Exhaust pressure to spin the turbine is increased, resulting in warming of the air compressed by the compressor. The warmed air is recirculated around the compressor and the CAC, thereby expediting warming of the CAC.
However, the inventors herein have recognized potential issues with such systems. As one example, icing of the CAC can also be observed in the case of shut-down, that is to say non-fired internal combustion engines, in particular if the internal combustion engine is generally operated only for short periods in the presence of temperatures below the freezing point. Large amounts of ice may form in the charge-air cooler, resulting from ice situated in the charge-air cooler that is not melted during operation, and additional ice is newly formed after every period of operation of the internal combustion engine.
In one example, the issues described above may be addressed by a method for a supercharged internal combustion engine having at least one cylinder head comprising at least one cylinder, in which each cylinder has at least one inlet opening which is adjoined by an intake line for the supply of air via an intake system, each cylinder has at least one outlet opening which is adjoined by an exhaust line for the discharge of the exhaust gases via an exhaust-gas discharge system, a charge-air cooler (CAC) is provided in the intake system, and an electrically driveable compressor is arranged in the intake system, the electrically driveable compressor being the compressor of an exhaust-gas turbocharger, and where the internal combustion engine has a bypass line, which branches off from the intake system, so as to form a first junction point, downstream of the electrically driveable compressor and downstream of the CAC and opens into the intake system, so as to form a second junction point, upstream of the electrically driveable compressor and upstream of the charge-air cooler. In this way, the CAC may be sufficiently warmed to melt ice formed within the CAC.
As one example, the electrically driveable compressor heats the air situated in the intake system during the compression, and conveys the heated air via the bypass line back to the intake side of said intake system, that is to say to the inlet of said intake system. The electric compressor may operate even when boost assistance to an exhaust turbocharger is not requested or during vehicle conditions where the vehicle is a hybrid electric vehicle operating in a low energy consuming mode. In this way, air may be recirculated through the electric compressor so that additional compression air results in a warming of the air. The warmed air may melt ice condensed in the CAC, thereby avoiding a decrease in the performance of the CAC. Air charging provided by the turbocharger compressor and electric compressor is maintained and degradation to the CAC is prevented.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.